End-to-end application via LAN (Local Area Network) or SAN (Storage Area Network) has been demanded to have high security and low latency. There is known a method by which encoding is performed while changing a synchronization bit pattern as desired in order to ensure reliability of end-to-end communication (for example, see Japanese Laid-open Patent Publication No. 9-55713). Because a receiving end receives a notification of the bit pattern from a transmitting end, the receiving end may read data in a frame-synchronous manner. Conversely, when the bit pattern is not known, frame synchronization is not achieved, and thus data may not be read.
By sending a plurality of bit patterns previously, encoding may be performed using frame synchronization according to the bit patterns. However, when the bit pattern is changed regularly, a synchronization bit pattern changing convention may be detected by monitoring the bit pattern, and thus the reliability of the encoding decreases.
When information resources are transmitted and received between data centers using an optical fiber, there is a problem in that it is difficult to increase the security level. Because a passive optical monitoring device such as an optical coupler is available at a low price, there is a concern that unauthorized branching of the fiber may be performed depending on an accessible region of the fiber. It is even difficult to detect such an unauthorized branching. Thus, it is desirable to develop a method for improving the security level other than just detecting and protecting against unauthorized branching of the fiber.
For example, there is a method utilizing an upper layer. In Internet Protocol Security Virtual Private Network (IPSec-VPN) using layer 3, data is encoded in encapsulation of a packet in VPN communication, and thus even if the communication line is wiretapped, the content or the sender of the data may not be identified. In addition, there is also a technique known as Secure Socket Layer Virtual Private Network (SSL-VAN) using layer 5.